Low-transition-temperature steel alloy



,LOW-TRANSI'I'ION-TEMPERATURE STEEL ALLOY Robert H. Frazier, Worthington, Ohio, assignor, by memo assignments, to the United States of America as represented by the Secretary of the Navy No Drawing. Application June 10, 1958 Serial No. 741,204

2 Claims. (Cl. 75-124) This invention relates to steel alloys and more particularly to hot-rolled killed low-alloy steel compositions of the type having superior low-transition-tcmperature properties.

It is well known in the field of metallurgy that varying temperatures of use of low-alloy steels can unfavorably affect the economics of using such steels for industrial equipment; Caution must therefore be used in selecting the proper type of steel for equipment which is to, be

used at low temperatures, in order to insure satisfactory performance over extended periods of operation. Improperly selected alloys may fail because of inadequate toughness and ductility, with the resultant loss of operating time and investment. The usual low-alloy steels, when cooled below room temperature, become less resistant to shock or impact and the resistance to impact decreases sharply when cooled below a critical temperature which is known as the transition temperature of the steel.

The present invention is directed to a steel composition or alloy which is an improvement over those disclosed in Bulletin Number 26 of April 1956 of Welding Research Council Series, published by the Welding Research Council of 29 West Thirty-ninth Street, New York 18, New York.

Accordingly, it is a particular object of this invention to produce a killed steel composition having superior low-transition-temperature properties.

Another object is to limit or correlate the aluminum and silicon contents of a killed steel alloy to provide lowtransition-temperature properties.

The present invention is based on the discovery that aluminum and silicon in selected proportions within a limited range have the effect of improving the low-transition-temperature properties of hot-rolled low-alloy killed steels. Alloys of the present invention have an aluminum content which is within the range of 0.03 to about 0.20 percent while the silicon content is within the range of 0.05 to about 0.47 percent and the alloys are prepared with the aluminum and silicon in substantially inverse quantities; that is, a major amount of alumimum and a minor quantity of silicon or a major quantity of silicon and a minor quantity of aluminum which may vary within the specified ranges. The quantity of aluminum and silicon combined totals approximately 0.25% to 0.50% of the entire steel composition and these components may exist in the composition in inverse quantities within the ranges above specified.

The following example discloses the range of the principal elements of an alloy steel within the scope of the present invention:

Typical examples of low-alloy steels prepared in accordance with the present invention are as follows:

Element Percent Transition Temperature Carbon 0. 21 "Man Qanesp 0. 75 Phosphorus 0. 015

1r 0. 025 -98 F. Nitro en 0. 004 Aluminum 0. 03 Silir'nn 0. 47

Element Percent Transition Temperature Qarhnn 0. 21 Man anese 0. 71 Phosphorus 0.018 Snlfm' 0. 027 69 F. Nitrogen 0. 003 Alnmln'nm' 0. 19 Silicon 0.05

Iron, of course, as is usual in steel alloy compositions, constitutes the base of the alloy and comprises substantially the remainder of the composition with the exception of insignificant amounts of compounds and impurities incident to usual steel making practice such as iron oxides, iron silicates, manganese sulfides, aluminum oxides and the like. The iron content with such steel alloys is usually of the order of 98 percent.

Steels, in accordance with the present invention, were prepared from a charge consisting of ingot iron and ferrosilicon equivalent to 0.10% silicon, and melted in an induction furnace under an atmosphere of argon to insure low, uniform nitrogen content. After the charge was melted at the desired temperature, the melt was partially deoxidized with standarddeoxidizing agents. Carbon, in the form of graphite, was added and the entire heat or mixture was poured directly into a suitable mold. The resulting ingots were heated to about 2250 F. and forged to slabs which were reheated to about 2250 F. and rolled to suitable gage for recharging into a furnace where they were maintained at a temperature at about 1850 F., for approximately 30 minutes and finally the slabs were rolled to produce inch sheets.

Keyhole Charpy specimens were taken parallel to the direction of rolling and were notched normal to the surface of the plate. The Charpy machine, from which impact data were obtained, had a total available striking energy of 220 ft.-lb. and a pendulum velocity of. 18.1 feet per second. The transition temperature was defined in these tests as the temperature at which the average energy-temperature curve crossed within the standard 12 ft.-lb. level. A bath of ethyl alcohol cooled by Dry Ice was used to obtain the desired temperatures for specimens tested below room temperature.

It has been found that comparable good impact strength transition temperatures may be obtained within the narrow ranges aforementioned between 60 to 100 F., provided that both aluminum and silicon are present and even though either may be varied in quantity between their respective prescribed ranges, for any one alloy these two elements should be present in substantially inverse quantities, i.e., minimum aluminum with maximum silicon or maximum aluminum with minimum silicon. For example, an alloy, in accordance with this invention, containing 0.05% silicon would require about 0.19% aluminum in order to obtain low-transition-temperature properties, as shown in the above chart.

From the above description, it will be apparent that there has been provided a novel low-alloy killed steel hav ing a low transition temperature while its other physical properties are not deleteriously affected. This characteristic qualifies this type steel, in accordance with this invention, for more extensive use than was possible with the old steel and particularly fits it for use in ship hull plate construction.

While there has been described a preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein within the scope of the invention, which is to be limited only by the appended claims.

What is claimed is:

1. A hot-rolled low-alloy killed steel composition hav'-.

phosphorus in the range of 0.014% to 0.020%,- snlfur in the range of 0.022% to 0.032%, nitrogen in the range V of 0.003% to 0.006%, aluminum in the range of 0.03%

ing an impact strength transition temperature below -'60 F., said steel consisting of carbon in the range of 0.18% to 0.22%, manganese in the range of 0.70% to 0.87%, phosphorus in the range of 0.014% to 0.020%, sulfur in the range of 0.022% to 0.032%, nitrogen in the range of 0.003% to 0.006%, aluminum in the range of 0.03%

to 0.22%, manganese in the range of 0.70% to 0.87%, 20

with the balance being substantially all iron.

2. A hot-rolled low-alloy killed steel composition hay-j ing an impact strength transition temperature below-60 F., said steel consisting of carbon in the range 650.18%

to 0.20%, silicon in the range of 0.05% to 0.47% with the balance being substantially all iron, and wherein both said aluminum and silicon are present and'preferably in substantially inverse quantities totaling approximately 0.25% to 0.50% of said composition. I

References Cited in the file of this patent 3 UNITED STATES PATENTS 2,402,135 Halley Iune 18, 1946 2,679,454 Olfenhauer May 25, 1954 2,797,162 Korczy'nsky June 25, 1957 2,845,345 Bauscher et a1 July 29, 1958 2,853,379 Althouse Sept.- 23, 1958 f FOREIGN PATENTS 786,993 Great Britain Nov. 27, 1957 I g OTHER REFERENCES. 'IH arty et. al.: Mining and Metallurgical Investigations,

Cooperative Bulletin 67, 1934. Published by the Mining and Metallurgical Advisory Boards, Carnegie Institute of to 0.22%, manganese in the range of 0.70% to 0.87%, 285 Technology, Pittsburgh, Pa. 

1. A HOT-ROLLED LOW KILLED STEEL COMPOSITION HAVING AN IMPACT STRENGTH TRANSION TEMPERATURE BELOW-60* F. SAID STEEL CONSISTING OF CARBON IN THE RANGE OF 0.18% TO 0.22% MANGANESE IN THJE RANGE OF 0.70% TO 0.87%, PHOSPHORUS IN THE RANGE OF 0.014% TO 0.020%, SULFUR IN THE RANGE OF 0.022% TO 0.032%, NITROGEN IN THE RANGE OF 0.003% TO 0.006%, ALUMINUM IN THE RANGE OF 0.03% TO 0.22%, MAGANESE IN THE RANGE OF 3.70% TO 0.87%, WITH THE BALANCE BEING SUBSTANTIALLY ALL IRON. 